rocks & weathering lesson 4
DESCRIPTION
TRANSCRIPT
![Page 1: Rocks & weathering lesson 4](https://reader034.vdocuments.net/reader034/viewer/2022042515/547842a45906b591318b4774/html5/thumbnails/1.jpg)
PHYSICALWEATHERIN
G
![Page 2: Rocks & weathering lesson 4](https://reader034.vdocuments.net/reader034/viewer/2022042515/547842a45906b591318b4774/html5/thumbnails/2.jpg)
Weathering
The decomposition and disintegration of rocks in situ.
![Page 3: Rocks & weathering lesson 4](https://reader034.vdocuments.net/reader034/viewer/2022042515/547842a45906b591318b4774/html5/thumbnails/3.jpg)
Decomposition
Refers to chemical weathering and creates changes in rock substances
For Example: Granite decompose into clay
![Page 4: Rocks & weathering lesson 4](https://reader034.vdocuments.net/reader034/viewer/2022042515/547842a45906b591318b4774/html5/thumbnails/4.jpg)
Disintegration
• Produces smaller, angular fragments of the same rocks, such as scree.
• No change in chemical composition.
• For example: Granite disintegrates into smaller fragment but rock type is still granite
![Page 5: Rocks & weathering lesson 4](https://reader034.vdocuments.net/reader034/viewer/2022042515/547842a45906b591318b4774/html5/thumbnails/5.jpg)
Erosion• Is the breaking
down and removal of rocks
• agents of erosion such as rivers, glaciers and the sea
![Page 6: Rocks & weathering lesson 4](https://reader034.vdocuments.net/reader034/viewer/2022042515/547842a45906b591318b4774/html5/thumbnails/6.jpg)
Denudation Weathering
and erosion working together causing landscape to be worn down
![Page 7: Rocks & weathering lesson 4](https://reader034.vdocuments.net/reader034/viewer/2022042515/547842a45906b591318b4774/html5/thumbnails/7.jpg)
Regolith
• a layer of loose material covering solid rock.
• It includes dust, soil, broken rock, and other related materials and is present on Earth, the Moon, some asteroids, and other terrestrial planets and moons.
![Page 8: Rocks & weathering lesson 4](https://reader034.vdocuments.net/reader034/viewer/2022042515/547842a45906b591318b4774/html5/thumbnails/8.jpg)
![Page 9: Rocks & weathering lesson 4](https://reader034.vdocuments.net/reader034/viewer/2022042515/547842a45906b591318b4774/html5/thumbnails/9.jpg)
• Weathering and erosion depend on each other
• One could not exist very effectively without the other
• Weathering break down a rock surface to produce a pile of loose debris (Regolith)
• Erosion then removes the broken down rock fragments often using the ‘weathered fragments’ as ‘tools’ for erosion.
• This exposes a fresh rock surface to the processes of weathering and so the two processes continue
![Page 10: Rocks & weathering lesson 4](https://reader034.vdocuments.net/reader034/viewer/2022042515/547842a45906b591318b4774/html5/thumbnails/10.jpg)
Three Types of Weathering
1. Physical Weathering
2. Chemical Weathering
3. Biological Weathering
![Page 11: Rocks & weathering lesson 4](https://reader034.vdocuments.net/reader034/viewer/2022042515/547842a45906b591318b4774/html5/thumbnails/11.jpg)
Physical Weathering
• Disintegration of rock into smaller particles by mechanical processes but without any change in the chemical composition of the rock
• Where is it likely to occur?- devoid of vegetation
- deserts, high mountains, arctic regions
• End product- sands
![Page 12: Rocks & weathering lesson 4](https://reader034.vdocuments.net/reader034/viewer/2022042515/547842a45906b591318b4774/html5/thumbnails/12.jpg)
Four main types of Physical / Mechanical Weathering
1. Freeze-thaw action / Frost Shattering / Ice crystal Growth
2. Salt crystalisation
3. Granular disintegration /Exfoliation
4. Pressure release
![Page 13: Rocks & weathering lesson 4](https://reader034.vdocuments.net/reader034/viewer/2022042515/547842a45906b591318b4774/html5/thumbnails/13.jpg)
1. When water within
the cracks freezes to
ice, its volume
expands as much as 9%.
2. This expansion creates a powerful force called frost action or freeze-thaw action, which can exceed the tensional
strength of rock.
Continuation of alternate freezing and thawing will cause joints and pores
enlarge and shatter.
Freeze thaw action
![Page 14: Rocks & weathering lesson 4](https://reader034.vdocuments.net/reader034/viewer/2022042515/547842a45906b591318b4774/html5/thumbnails/14.jpg)
![Page 15: Rocks & weathering lesson 4](https://reader034.vdocuments.net/reader034/viewer/2022042515/547842a45906b591318b4774/html5/thumbnails/15.jpg)
![Page 16: Rocks & weathering lesson 4](https://reader034.vdocuments.net/reader034/viewer/2022042515/547842a45906b591318b4774/html5/thumbnails/16.jpg)
![Page 17: Rocks & weathering lesson 4](https://reader034.vdocuments.net/reader034/viewer/2022042515/547842a45906b591318b4774/html5/thumbnails/17.jpg)
Factors encouraging Frost Shattering / Freeze Thaw action
• Rapid freezing with a minimum temperature of -50C
• Frequent cycle of freeze thaw actions
• High degree of porosity or density of cracks in a rock
• Presence of water
![Page 18: Rocks & weathering lesson 4](https://reader034.vdocuments.net/reader034/viewer/2022042515/547842a45906b591318b4774/html5/thumbnails/18.jpg)
Salt-crystal growth (haloclasty)
• causes disintegration of rocks
• saline solutions seep into cracks and joints in the rocks and evaporate, leaving salt crystals behind.
• salt crystals expand as they are heated up, exerting pressure on the confining rock.
• may also take place when solutions decompose rocks
• Example: limestone and chalk to form salt solutions of sodium sulfate or Sodium carbonate, when the moisture evaporates to form salt crystals.
![Page 19: Rocks & weathering lesson 4](https://reader034.vdocuments.net/reader034/viewer/2022042515/547842a45906b591318b4774/html5/thumbnails/19.jpg)
Salt weathering of sandstone near Qobustan, Azerbaijan.
Salt weathering of building stone on the island of Gozo, Malta
![Page 20: Rocks & weathering lesson 4](https://reader034.vdocuments.net/reader034/viewer/2022042515/547842a45906b591318b4774/html5/thumbnails/20.jpg)
Insolation weathering / heating and cooling
• Expansion and contraction of rock particles resulting from extreme variations in temperature
• Significant in desert area where diurnal temperature range is high (400C – 500C)
![Page 21: Rocks & weathering lesson 4](https://reader034.vdocuments.net/reader034/viewer/2022042515/547842a45906b591318b4774/html5/thumbnails/21.jpg)
![Page 22: Rocks & weathering lesson 4](https://reader034.vdocuments.net/reader034/viewer/2022042515/547842a45906b591318b4774/html5/thumbnails/22.jpg)
![Page 23: Rocks & weathering lesson 4](https://reader034.vdocuments.net/reader034/viewer/2022042515/547842a45906b591318b4774/html5/thumbnails/23.jpg)
Pressure release
• It is not caused by element of the weather. However, it does occur in situ
• Involve the disintegration of rocks to expand
• Pressure release can be caused:i. Erosion of overlying rockii. When huge ice sheets melt at the end of a
glacial period
![Page 24: Rocks & weathering lesson 4](https://reader034.vdocuments.net/reader034/viewer/2022042515/547842a45906b591318b4774/html5/thumbnails/24.jpg)
Pressure release:
• common in intrusive rocks that were formed deep under ground.
• E.g. granite batholiths.
• When this rock is exposed to the surface by uplift and erosion the rock expands and sheet joints form parallel to the rock surface.
![Page 25: Rocks & weathering lesson 4](https://reader034.vdocuments.net/reader034/viewer/2022042515/547842a45906b591318b4774/html5/thumbnails/25.jpg)
![Page 26: Rocks & weathering lesson 4](https://reader034.vdocuments.net/reader034/viewer/2022042515/547842a45906b591318b4774/html5/thumbnails/26.jpg)
WWhat type of weathering?
![Page 27: Rocks & weathering lesson 4](https://reader034.vdocuments.net/reader034/viewer/2022042515/547842a45906b591318b4774/html5/thumbnails/27.jpg)
What type of weathering?
![Page 28: Rocks & weathering lesson 4](https://reader034.vdocuments.net/reader034/viewer/2022042515/547842a45906b591318b4774/html5/thumbnails/28.jpg)
What type of physical weathering?
![Page 29: Rocks & weathering lesson 4](https://reader034.vdocuments.net/reader034/viewer/2022042515/547842a45906b591318b4774/html5/thumbnails/29.jpg)
Classwork
• Ross pg 51 – Noting activity